This invention relates to novel, light sensitive, photoresist materials which are used in the photo-engraving process or in the production of the phosphor screens of color picture tubes.
Light sensitive photoresist compositions which change their solvent solubility on exposure to light, are used for precision processing in the photo-engraving process or in the production of the phosphor screens of color picture tubes.
These light sensitive photoresist compositions are roughly divided in two types, namely the water-insoluble type and the water-soluble type, the choice between which depends on the intended use.
Water-insoluble light sensitive photoresist compositions require the use of organic solvents, and, in view of the cost and toxicity of these organic solvents, they recently tend to be replaced by water-soluble light sensitive photoresist compositions.
A typical example of a well-known water-soluble light sensitive photoresist composition is a mixture comprising a water-soluble polymer, such as gelatin and polyvinyl alcohol, and a dichromate such as ammonium dichromate. This mixture becomes water-insoluble on exposure to light. However, this light sensitive photoresist composition undergoes chemical changes at room temperature even with no exposure to light. It is therefore, defective in that its light sensitive characteristics are diminished when it is stored for a long time.
As a means of overcoming this defect, it has been proposed that an azide compound be used instead of the dichromate. A mixture of a water-soluble polymer and an azide compound is characterized in that it is quite stable in the dark and in that it can be stored for a long time without diminishment of the light sensitive characteristics.
Among the azide compounds that can be used as one component of the light sensitive photoresist composition, disodium 4,4'-diazidostilbene-2,2'-disulfonate is especially suitable for use in combination with a water-soluble polymer and is widely used in the way.
When a mixture of this azide compound and a water-soluble polymer is exposed to light rays of a suitable wavelength, the azide compound absorbs the light energy and decomposes. The decomposition product cross-links the polymer molecules to render the polymer water-insoluble. This insolubilization reaction does not occur at room temperature unless the mixture is exposed to light.
However, the azide compound only absorbs light rays at a wavelength of about 300 to 360 nm. Therefore, a photoresist composition comprising a mixture of this azide compound and a water-soluble polymer does not have too high of a sensitivity to light.
Furthermore, this azide compound is unreactive to polyvinyl alcohol (PVA) which has excellent physical properties, such as adhesion, when coated onto a suitable support material.
As for the known azide compounds that show a higher light sensitivity than the above-mentioned azide compound, there can be cited, for examples, the condensation products of p-azidobenzaldehyde with an aliphatic or an aromatic ketone such as acetone or cyclohexanone. However, these azide compounds are insoluble in water. Accordingly, it may be stated that no water-soluble light sensitive photoresist compositions can be obtained by mixing these condensed azide compounds with water-soluble polymers.